A new system has been developed in accordance with the recent advances of information processing, information storage and image processing technologies as well as the spreading utilization of communications circuits. It is a technique of producing hard copies from soft information involving photoelectric conversion of electrical signals onto photosensitive material, thereby reproducing image information given in the form of a photograph, characters or numerals into a visible image.
This new system is commercially utilized in a variety of applications including facsimile, computer-aided phototype setting system, characer composing system, scanner dot image formation, holography, and IC photomask.
Equipment for these rapid information transmitting systems include light sources which are often xenon flash lamps, glow discharge lamps, arc lamps, high-pressure mercury lamps, xenon lamps, cathode ray tubes providing flying spots in their phosphor, light emitting diodes (LED) and lasers. Any of these high illuminance light sources is combined with a high speed shutter to provide a light source assembly.
On the other hand, with the advances of both photographic silver halide photosensitive material and a compact, simple, rapid development system which is known as a mini-labo system, photographic prints of high image quality are readily available at low cost. There is a strong demand for producing hard copies from soft information sources in a simple inexpensive manner while retaining an image quality equivalent to photographic prints.
Prior art means for producing hard copies from soft information sources are generally classified into two, one means not relying on photosensitive recording materials, such as systems using electrical and electromagnetic signals and ink jet printing systems and another means using photosensitive materials such as silver halide photosensitive materials and electrophotographic materials. The latter is a recording means using an optical system which is controlled in accordance with image information to emit radiation while the optical system itself is advantageous for providing high image quality because of resolving power, binary recording and multi-gradation recording. As compared with the system using electrophotographic material, the system using photographic silver halide photosensitive material is advantageous because of chemical image formation. The system using photographic silver halide photosensitive material, however, requires deliberate efforts in establishing or optimizing the sensitive wavelength compatible with the optical system, stability of sensitivity, stability of latent images, resolving power, color separation of three primary colors, rapidness and ease of color development, and cost.
Prior art color duplicating techniques include duplicating machines and laser printers based on the electrophotographic technology, dye diffusion systems using heat-developable silver halide material, and Pictrography (trade name of Fuji Photo-Film Co., Ltd.) using LED.
Heat-developable photosensitive material is well known in the art. The heat-developable photosensitive material and its process are described in the literature and patents, for example, "Shasinkougaku No Kiso --Higinen Shasin--" ("Fundamentals of Photographic Engineering --Non-Silver Salt Photography--"), 1982, Corona Publishing K. K., pages 242-255 and U.S. Pat. No. 4,500,626 which is incorporated herein by reference. In addition, U.S. Pat. Nos. 3,761,270 and 4,021,240 disclose a method of forming dye images through coupling reaction with an oxidant of a developing agent. U.S. Pat. No. 4,235,957 discloses a method of forming positive color images by a photosensitive silver dye bleaching technique.
It was also proposed to imagewise release or form a diffusible dye through heat development and transfer the dye to a dye fixing element. With this technique, either negative or positive dye images can be obtained by selecting a suitable type of dye-providing compound or a suitable type of silver halide. For detail, reference is made to U.S. Pat. Nos. 4,500,626, 4,483,914, 4,503,137, 4,559,290; Japanese Patent Application Kokai (JP-A) Nos. 149046/1983, 218443/1984, 133449/1985, and 238056/1986; EP 210660 A2 and 220746 A2; Japan Invention Society's Kokai Giho (Technical Report) No. 87-6199 and the like.
A variety of proposals have been made in the art for producing positive color images through heat development. For example, U.S. Pat. No. 4,559,290 proposes a method for forming an image by converting a dye providing (DRR) compound into an oxidized form having no dye releasing ability, preparing a heat-developable material in which the oxidized DRR compound is co-present with a reducing agent or a precursor thereof, carrying out heat development to oxidize the reducing agent in an amount corresponding to the exposure of silver halide, and allowing the remainder of the reducing agent unoxidized to reduce the oxidized DRR compound into the DRR compound to release a diffusible dye. EP 220746 A2 and Technical Report No. 87-6199 (Vol. 12, No. 22) describe a compound capable of releasing a diffusible dye through a similar mechanism, more particularly a heat-developable color photosensitive material using a compound capable of releasing a diffusible dye through reductive cleavage of an N-X linkage where X is an oxygen, nitrogen or sulfur atom.
Conventional color photosensitive materials generally have spectral sensitization in blue, green and red. In order to produce images in such color photosensitive materials from the image information which has been converted into electrical signals, color cathode ray tubes (CRT) are generally used as an exposure light source. Unfortunately, CRTs are inadequate to produce large size prints.
Also light emitting diodes (LED) and semiconductor lasers (LD) have been developed as the write-in head capable of producing large size prints. However, none of the optical write-in heads ever developed can efficiently emit blue light. Thus in the case of light emitting diodes (LED), for example, a light source in the form of a set of three light emitting diodes of near-infrared (800 nm), red (670 nm) and yellow (570 nm) must be used for exposure of a color photosensitive material having three layers which are spectrally sensitized in near-infrared, red and yellow. One image recording system of such construction is described in Nikkei New Material, Sep. 14, 1987, pp. 47-57 and some are used in commercial application.
Similarly, a system including a light source in the form of a set of three semiconductor lasers of 880 nm, 820 nm and 760 nm light emission for recording images in a color photosensitive material having three photosensitive layers which are sensitive to the respective wavelengths is described in JP-A 137149/1986.
In general, when the colors of yellow, magenta and cyan are generated in a multilayer color photosensitive material by exposure to three different spectra, it is of importance for color reproduction to generate the respective colors without amalgamation. Particularly when light emitting diodes (LED) and semiconductor lasers (LD) are used as the exposure light source, the photosensitive material must be designed to have three spectral sensitivities in spectra within the narrow range between the red end and the infrared region. It is a key for improving color separation to reduce the overlap between the respective spectral sensitivities as much as possible.
Since the sensitizing dyes of the near-infrared to infrared region which have been heretofore used are very broad in spectral sensitivity, there is a likelihood for their spectral sensitivities to overlap one another, leading to poor color separation.
To insure color separation, attempts were made to sequentially increase the sensitivity from a shorter wavelength side or to provide filter layers as described in U.S. Pat. No. 4,619,892. However, the sequential increase of sensitivity can invite increased fog and adversely affect raw stock stability. In addition, the infrared sensitization is known to inherently deteriorate the raw stock stability of photosensitive material. There is a need for a photosensitive material having sharp spectral sensitivity and high sensitivity in the infrared region.
For sharp spectral sensitivity, a choice of the spectral sensitivity peak wavelength becomes more important than in the case of broad spectral sensitivity. This means that to provide higher sensitivity, the spectral sensitivity peak wavelength must be set near the light emission wavelength of a semiconductor laser or light emitting diode.
During operation, the semiconductor lasers experience an intensity lowering or droop accompanied by ah increase of the light emission wavelength due to self heat generation. In the event of sharp spectral sensitivity, if the spectral sensitivity peak wavelength is shorter than the light emission wavelength of the semiconductor laser, then a lowering of density upon delivery of image outputs due to the droop is considerably expanded. Therefore, the spectral sensitivity peak wavelength must be set longer than the light emission wavelength of the semiconductor laser for compensating for the density lowering due to the droop. In the event of sharp spectral sensitivity, control of the peak wavelength is thus a very important problem in the design of photosensitive material.
There is a need to have a photographic silver halide photosensitive material having sharp spectral sensitivity and high sensitivity in the infrared region.